1. Field of the Invention
The present invention relates to an improved clutch facing, and more particularly to a method of manufacturing a clutch facing of the type used for automotive automatic transmissions or the like.
2. Description of the Prior Art
Clutch facings of the type used for automotive automatic transmissions are usually made of a paper based frictional material which contains some additional components which improve the frictional qualities such as the friction coefficient of the facing, and/or the durability of the facing against wear.
The conventional method of manufacturing a paper based frictional material (hereinafter referred to as a frictional material) which is known as the wet method incorporates a resin in the liquid state as a binder agent.
Frictional materials produced by the conventional wet method are obtained by mixing a wood pulp together with a lubricant, an organic fiber, and other ingredients in a mixing device, and forming paper from the mixture with a paper machine. Thereafter, a paper object of the required shape is stamped from the paper by a paper stripper such as a crank press. The stamped paper piece is soaked in a solution of a binder agent such as a phenolic resin in a solvent and then is dried. The dried product is preheated in a drying furnace and then the pre-heated product is placed in contact with a core plate in the presence of an adhesive agent. The laminate is pressed and heated in a metal mold installed in a press molding machine, followed by heating the product in a drying furnace, thereby obtaining the complete frictional material. The purpose of heating the laminate in the drying furnace is to ensure completion of curing of the binder and adhesive agents.
The frictional material contains a lot of wood pulp and organic materials such as organic fiber and the binder agent so that a product of somewhat desirable frictional qualities can be obtained. The desirable frictional qualities are fulfilled by carbonizing portions of the wood pulp and the like. However, in the conventional method of manufacturing the frictional material, heating of the product is performed in the air, which results in oxidative deterioration of the material. Consequently, the heating step must be terminated before the desired extent of carbonization of the wood pulp and the like is attained. Accordingly, a frictional material of completely satisfactory frictional qualities is not yet available.
The conventional method described above presents other difficulties in that it brings about a low initial value of the frictional coefficient of the material, thereby resulting in the phenomenon of bedding. The term "bedding" as used herein is the quality of transmission caused by the frictional material. Because the material exhibits a low initial frictional coefficient, the frictional material may not achieve its frictional coefficient of desired constant value until after many hours of use. In the meantime a squeezing noise (crank noise) is often heard. It is believed that the crank noise is heard if the ratio of the static coefficient to the dynamic coefficient of the frictional material is above 1.30. Therefore, a need continues to exist for a method of preparing a frictional material which will immediately exhibit the desired frictional coefficient value.